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<topic_start>Why BuildContext requires extra attention |
An example of a large, short-living object that |
might squeeze into a long-living area and thus cause leaks, |
is the context parameter passed to Flutter’s |
build method.The following code is leak prone, |
as useHandler might store the handler |
in a long-living area:<topic_end> |
<topic_start>How to fix leak prone code? |
The following code is not leak prone, |
because:<topic_end> |
<topic_start>General rule for BuildContext |
In general, use the following rule for a |
BuildContext: if the closure doesn’t outlive |
the widget, it’s ok to pass the context to the closure.Stateful widgets require extra attention. |
They consist of two classes: the widget and the |
widget state, |
where the widget is short living, |
and the state is long living. The build context, |
owned by the widget, should never be referenced |
from the state’s fields, as the state won’t be garbage |
collected together with the widget, and can significantly outlive it.<topic_end> |
<topic_start> |
Memory leak vs memory bloat |
In a memory leak, an application progressively uses memory, |
for example, by repeatedly creating a listener, |
but not disposing it.Memory bloat uses more memory than is necessary for |
optimal performance, for example, by using overly large |
images or keeping streams open through their lifetime.Both leaks and bloats, when large, |
cause an application to crash with an out-of-memory error. |
However, leaks are more likely to cause memory issues, |
because even a small leak, |
if repeated many times, leads to a crash.<topic_end> |
<topic_start> |
Memory view guide |
The DevTools memory view helps you investigate |
memory allocations (both in the heap and external), |
memory leaks, memory bloat, and more. The view |
has the following features:<topic_end> |
<topic_start> |
Expandable chart |
The expandable chart provides the following features:<topic_end> |
<topic_start>Memory anatomy |
A timeseries graph visualizes the state of |
Flutter memory at successive intervals of time. |
Each data point on the chart corresponds to the |
timestamp (x-axis) of measured quantities (y-axis) |
of the heap. For example, usage, capacity, external, |
garbage collection, and resident set size are captured.<topic_end> |
<topic_start>Memory overview chart |
The memory overview chart is a timeseries graph |
of collected memory statistics. It visually presents |
the state of the Dart or Flutter heap and Dart’s |
or Flutter’s native memory over time.The chart’s x-axis is a timeline of events (timeseries). |
The data plotted in the y-axis all has a timestamp of |
when the data was collected. In other words, |
it shows the polled state (capacity, used, external, |
RSS (resident set size), and GC (garbage collection)) |
of the memory every 500 ms. This helps provide a live |
appearance on the state of the memory as the application is running.Clicking the Legend button displays the |
collected measurements, symbols, and colors |
used to display the data.The Memory Size Scale y-axis automatically |
adjusts to the range of data collected in the |
current visible chart range.The quantities plotted on the y-axis are as follows:<topic_end> |
<topic_start> |
Profile Memory tab |
Use the Profile Memory tab to see current memory |
allocation by class and memory type. For a |
deeper analysis in Google Sheets or other tools, |
download the data in CSV format. |
Toggle Refresh on GC, to see allocation in real time.<topic_end> |
<topic_start> |
Diff Snapshots tab |
Use the Diff Snapshots tab to investigate a feature’s |
memory management. Follow the guidance on the tab |
to take snapshots before and after interaction |
with the application, and diff the snapshots:Tap the Filter classes and packages button, |
to narrow the data:For a deeper analysis in Google Sheets |
or other tools, download the data in CSV format.<topic_end> |
<topic_start> |
Trace Instances tab |
Use the Trace Instances tab to investigate what methods |
allocate memory for a set of classes during feature execution:<topic_end> |
<topic_start>Bottom up vs call tree view |
Switch between bottom-up and call tree views |
depending on specifics of your tasks.The call tree view shows the method allocations |
for each instance. The view is a top-down representation |
of the call stack, meaning that a method can be expanded |
to show its callees.The bottom-up view shows the list of different |
call stacks that have allocated the instances.<topic_end> |
<topic_start> |
Other resources |
For more information, check out the following resources: |
<topic_end> |
<topic_start>Using the Debug console |
The DevTools Debug console allows you to watch an |
application’s standard output (stdout), |
evaluate expressions for a paused or running |
app in debug mode, and analyze inbound and outbound |
references for objects.info Note |
This page is up to date for DevTools 2.23.0.The Debug console is available from the Inspector, |
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